From Alaska to the Andes, there is no question that the world is getting hotter –FAST. Globally, the temperature is up 1 degree Fahrenheit over the past century, but some of the coldest, more remote spots have warmed much more. The results are harrowing. In a three-part documentary report, the cover story for the September issue of National Geographic magazine focuses on the biggest issue facing the environment today: global warming and its effects. Four years in the making, this astounding story traverses the globe, pinpointing the physical and ecological signs of climate change (both stunning and subtle) and revealing what abrupt climate changes in the past are telling us about our own future.

Warnings about climate change can sound like an environmentalist scare tactic, meant to force us out of our cars and cramp our lifestyles, but National Geographic reveals the cold hard facts on the ground, and the Earth has disturbing news. Global warming is happening. Things that normally happen in geologic time are happening during the span of a human lifetime.

Doubters say that climate is notoriously fickle, that recent anemic snowfalls and five-year-long droughts are part of a passing phase. Leading scientists counter, “Don’t bet on it.” The level of carbon dioxide today is higher than it has been for hundreds of thousands of years. That we are changing the climate is undeniable. What’s worse, even if we stopped our CO2 emissions this instant, we are already committed to a warmer world. And experts fear that the warming may not be gradual, but could accelerate into a devastating climate lurch, giving us little or no time to adapt.

Scientists long ago predicted that the most visible impacts from a globally warmer world would occur first at high latitudes: rising air and sea temperatures, earlier snowmelt, later ice freezes, reductions in sea ice, thawing permafrost, more erosion, increases in storm intensity. Now all those impacts have been documented in Alaska, a canary in the coal mine of climate change. The drastic changes observed there by scientists and reported and photographed by National Geographic provide an early-warning system for the planet.

Dividing the report into three parts –GeoSigns, EcoSigns and TimeSigns –National Geographic magazine presents an unprecedented view of global warming.

GeoSigns: Data from the last 100-150 years show just how drastic the climate changes are.

-Winters are shorter now: Freshwater ice breakup in the Northern Hemisphere now occurs nine days earlier.

-Global average sea level has risen between 4 and 8 inches worldwide –over the past 100 years, the average rate of sea level rise has been around a tenth of an inch a year. This continually increasing sea level has great potential for reshaping coastlines and displacing more than
100 million people worldwide. (Every inch of sea level rise could cause shorelines to move inland by 8 feet.)

-Ocean temperatures are rising in all ocean basins and at much deeper depths than previously thought, according to NOAA scientists.

-Many rivers are getting less water than a century ago due to earlier snowmelt in the spring and less snow falling overall. In California, the reduced water input is as much as 12 percent.

-The people of Wisconsin are losing winter as they know it. Lakes in the state are now frozen
up to 25 percent less time.

-In Alaska, the breakup of sea ice off the coast happens weeks earlier than it once did. Since 1978, the area of perennial Arctic sea ice has declined 9 percent per decade.

EcoSigns: Animals and plants are coping with the heat –or they’re not. As the planet warms, plants are flowering sooner and trees are shedding their leaves earlier. Habitats are changing, causing migration schedules, births, and food cycles of animals and plants to shift out of sync.

-The Adelie penguin colony on the Antarctic Peninsula has dropped by five-sixths from 1900 to 2004 due to a 9 degree increase in temperature over the past 50 years and severe retreating of sea ice. Just since the 1960s, the number of breeding pairs has dropped by two-thirds. Of the Antarctic ecosystem, scientists state, “It has gone to hell.”

-Tree swallows in North America migrate north in the spring 12 days earlier than 25 years ago.

-Scientists have long known that hot weather during the incubation phase causes turtles’ eggs to yield more females. What’s surprising is that they have now detected a gender imbalance in sea turtles in favor of females worldwide.

-Researchers have seen 15 percent body mass declines in polar bears in the Hudson Bay region. The bears are not getting as much food as they used to because of the loss of sea ice from which they hunt seals and fish. If ice loss trends continue, polar bears will either move to the high Arctic or have to learn to hunt caribou.

-Caribou herd numbers have dropped from 178,000 in 1989 to 123,000 in 2001. Scientists believe that global warming may be the cause, as the necessary plants they eat at calving time are growing earlier and dieing back before the caribou can eat enough to gain body fat to survive the winter.

TimeSigns: Today, scientists are working to understand what has caused –and what will cause again –the sudden climate changes that Earth periodically undergoes. Not the 100,000-year fluctuations, but the more rapid shifts that scientists have recently identified when the Earth switches like a light from frozen Ice Age to picnic-warm and back again. How often and how quickly have such dramatic changes happened? What do these reversals tell us about the direction of Earth’s climate today and in the future? Only by understanding past linkages among the ocean, atmosphere and biosphere, and determining which the really big players were in past sudden change, can we better deal with future surprises.

Presenting the hard truth about global warming as scientists see it, National Geographic magazine lays a firm foundation upon which the growing debate over fossil fuels and the environment takes place.